In recent years, mouse and human iPS cells have been established one after another. Yamanaka et al. induced iPS cells by transferring the Oct3/4, Sox2, Klf4 and c-Myc genes into mouse and human fibroblasts, and forcing the cells to express the genes [1-3]. Thomson et al. produced human iPS cells using Nanog and Lin28 in place of Klf4 and c-Myc [4, 5]. However, the efficiency of iPS cell establishment was low at less than 1%.
Various efforts to improve the efficiency of iPS cell establishment have been made. For example, the present inventors reported that the inhibition of p53-p21 pathway remarkably increased the efficiency of iPS cell establishment [6, 7]. Maekawa et al. reported that the efficiency of iPS cell establishment was remarkably improved by transferring Glis1 along with Oct3/4, Sox2 and Klf4 into a somatic cell [8, 9]. In addition, it was found that Glis1 inhibits the proliferation of cells with imperfect reprogramming but only proliferates completely reprogrammed ones. They found that Glis1 was able to facilitate reprogramming by increasing the expressions of several genes that are reported to be involved in reprogramming.